But what did the study really show? And what are ‘chemical jobs’ anyway? We wanted to clear up one or two things about the study, and who is and isn’t at risk because of their job.

The study

The researchers, who were based in Ontario in Canada compared 1,006 women with breast cancer and 1,146 women without, to see whether those with breast cancer were more likely to work in particular jobs than others. They looked at a huge range of different jobs, from agriculture to wood manufacturing and bar/gambling work.

The findings were reported as showing that women in certain jobs, including those with chemical exposures and bar/gambling work, had a higher risk of breast cancer. But there were a number of limitations with the study that mean those headlines simply weren’t justified.

Small numbers

For a start, because the researchers looked at so many different types of job, the numbers of women in each group were tiny. This is a real problem because it makes it much harder to generalise to the whole population when the result’s only based on a few people.

For example, the analysis suggested that women working in agriculture were more likely to have breast cancer. But only 42 women with breast cancer had worked in agriculture. And in automotive plastics manufacturing, another job where women seemed to have a higher risk, only 26 women with breast cancer were included. These numbers are far too small to start drawing firm conclusions from.

The researchers did say that women in these jobs had a higher breast cancer risk. But the result they found (as well as being based on only 16 women with breast cancer) wasn’t statistically significant – that’s to say, the researchers weren’t able to be confident that this result was real, and it could easily have just happened by chance.

This means we can’t conclude anything at all about the risk of breast cancer related to these jobs. A final important limitation of the research is that the scientists didn’t actually measure specific exposures to chemicals in the different jobs.

Taken together, these several drawbacks mean that it’s difficult to conclude anything particularly meaningful from the study.

What do other studies say?

But we do know that some jobs can put people at higher risk of cancer – there’s a lot of evidence showing that people in industries like the manufacturing industry, are more likely to be exposed to chemicals that can raise their cancer risk.

For example, a recent study estimated that around 8,000 cancer deaths each year in the UK are down to exposure to harmful chemicals in the workplace. And just under half of these deaths are among male construction workers who are most likely to come into contact with asbestos as well as other important carcinogens such as silica and diesel engine exhaust.

It’s certainly important to understand how such ‘occupational exposures’ affects cancer risk – not least because this can help inform guidelines and regulations that protect workers. But it’s equally important to be clear and evidence-based, not only about which jobs can affect people’s cancer risk, but also how employers and employees can work together to reduce that risk.

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